Rodgers emphasized that children take their cues about what is happening from the adults around them. That's why it's very helpful for adults to stay calm, so the children see that and stay calm as well.

Children exiting Cajon High School were seen skipping and giving high-fives to the adults around them, because the adults set a calm example.

What is the most important thing for parents to keep in mind? Rodgers said they should reassure their children that they're safe at home and at school most of the time, and these types of events, while very upsetting, are very rare.

Rodgers noted that the adults on scene at Cajon High did the right thing by keeping things positive.

She said it's also important that the students are given the opportunity to think and talk about what they experienced, and what it was like for them -- including parts that were both scary and positive.

What about the children who witnessed the shooting in that classroom and their parents?

As for those parents, Rodger's gave this advice: watchful waiting.

"The vast majority of people exposed to even to really terrible traumatic events have a period of upset - that's normal, we would expect that - but then return to their usual way of being," she said.

She added that it's only a small fraction of people who have ongoing difficulty in coping following terrible trauma.

What if the child is scared to go back to school?

Students as well as parents may be scared about returning to school following such a traumatic incident. Roodgers said children need to be reassured that such incidents are rare, and parents need to emphasize that there are strong plans in place so children are kept safe in schools. Again, Rodgers stressed that children take cues from their parents.

"A parent's ability to stay calm and kind of take a step back and think through a situation makes a big difference in how a child copes," she explained.

How about parents who are overly fearful? Rodgers said it's normal for people to feel very upset short term - but if such feelings linger for a couple of weeks, that's when the parent and/or student should consider seeking professional help.

"There are mental health treatments available for children from infancy on up, so there are things that we can do for folks who are struggling, and even very young children, we now know, struggle sometimes from the effect of exposure to ongoing stress and trauma," she said.

As for those students who were in the classroom when the gunfire erupted, Rodgers said those children can go on to have happy, successful lives with good support in coping with what they've been through.

"It's going to be part of their story, but only a part of their story," she said.